This application seeks funding to capitalize on an extraordinary opportunity to create a demographic database comprising all residents of the United States in 1850. This massive new database will fill a critical gap in American population data infrastructure. The 1850 data collection will provide a baseline for studies of fertility and mortality in the United States before the onset of deliberate fertility control and mortality decline. As the earliest national microdata resource, the database will also be the initial observation for studies of migration, labor markets, wealth distribution, disability, education, and a host of other economic and demographic issues. A database incorporating the entire 1850 census will open an array of new research topics and methodological approaches to the study of long-run demographic change, ranging from the study of the oldest-old to multi-level analysis. The complete-count 1850 database is feasible because of a remarkable data-collection effort by the Church of Jesus Christ of Latter Day Saints (LDS). This initiative involved approximately 50,000 LDS volunteers who invested over one million hours to transcribe 23 million 1850 census records describing the free population, slaves, and deaths in the year prior to the census. The LDS has agreed to provide these remarkable resources free of charge to create and disseminate a database for scientific research and educational purposes. The first goal of the project is to augment and clean raw transcriptions of the 1850 censuses, adding omitted variables and improving data quality. The second goal is to transform these enhanced transcriptions into a data suitable for statistical analysis, and integrate them with the existing data collections disseminated by the Minnesota Population Center. Old census data are not of purely historical interest;they are essential tools for basic social research and policy analysis. Models and descriptions based on historical experience underlie both theories of past change and projections into the future. These data provide a unique laboratory for the study of economic and demographic processes. This kind of empirical foundation is essential for testing social and economic theory. This database is directly relevant to the central mission of the NIH as the steward of medical and behavioral research for the nation: the new data will advance fundamental knowledge about the nature and behavior of human population dynamics. This basic infrastructure will stimulate health-related research on population growth and movement, fertility, mortality, and nuptiality, as well as the economic and social correlates of demographic behavior. PUBLIC HEALTH RELEVANCE: The baseline microdata infrastructure is directly relevant to the central mission of the NIH as the steward of medical and behavioral research for the nation: the new data will advance fundamental knowledge about the nature and behavior of human population dynamics. This basic infrastructure will stimulate health- related research on population growth and movement, fertility, mortality, and nuptiality, as well as the economic and social correlates of demographic behavior.